1. Field of the Disclosure
The present disclosure relates generally to electrophotographic printers and, in particular, to a mechanism used to deskew imaging drums and an intermediate transfer belt module while maintaining mutual planarity between them.
2. Description of the Related Art
In electrophotographic (EP) printers, maintaining the plane of major EP systems, such as an intermediate transfer belt (ITB) module is essential to creating quality printed images. The plane of an ITB module is established by the mounting of the two rolls around which the ITB travels. The shafts of two rolls are mounted to opposed panels of a frame of the printer. In its simplest form the frame is comprised of a front and rear panel interconnected by two side panels, all of which are mounted to a bottom panel. When all of the panels are assembled together a small amount of twist or racking may occur due to manufacturing tolerances. For example one end of the front panel may be racked or twisted with respect to the rear panel by about 1.0 to 1.5 mm either in an upward or positive direction or in a downward or negative direction with respect to horizontal.
Using the rear panel as a reference plane, the mounting of the shafts of the two rolls therein establish two of the datum points needed to establish the plane of the ITB module. The third datum point is one of the two mounting locations in the front panel for the two shafts of the two rolls. However, due to the racking of the front panel, the remaining shaft end when mounted to the front panel will be either slightly above or below the plane established by the other three shaft ends resulting in a skewing of the ITB module. Situated either above or below the ITB module are four imaging drums that are designed to be in contact with the surface of the ITB and designed to lie in a common plane. The four imaging drums have their shafts mounted to the front and rear panels. Due to the racking of the front panel, the amount that each imaging drum is moved out of its common plane increases as the mounting location of the imaging drum nears the racked end of the front panel.
To correct the nonplanar position of the fourth shaft end of the roll in the ITB module so that it lies in the plane established by the first three shaft ends, an upward or downward biasing force is applied to the fourth shaft end, depending the direction in which the racking occurs, to move and hold the fourth shaft end in the plane of the ITB module. This adjustment ensures that the ITB module is essentially flat or planar. As the flatness of ITB varies from zero, the walk rate of the ITB increases the stress on the edges thereof. This increased stress induces cracks and ultimately results in failure of the ITB.
However, this solution of leveling the ITB module does not address the non-planarity of the imaging drums which may lead to print quality issues. The non-planarity introduces variations in the focal distances from the laser scan unit print head to each of the imaging drum surfaces which negatively impacts print quality. While the flatness of the plane of the ITB module may be readily adjusted by a single biasing mechanism, such a solution is not possible for the four imaging drums in that at least three shafts and possibly four shaft would need to be adjusted. With the prior art arrangement at least three adjustment mechanisms for the shaft ends of three of the imaging drums would be needed as the amount of non-planarity in the imaging drum most distant from where the highest racking occurs may be within acceptable tolerances. In a worst case, four adjustment mechanisms would be needed.
Accordingly, it would be advantageous to provide an assembly where the planarity of the ITB module may be accomplished while also being able to retain the parallel planar relationship between the ITB module and the plane of the imaging drums. It would be a further advantage to be able to accomplish the foregoing with a single adjustment.